Glass wool molded products are lightweight and have functions such as heat insulating properties, sound insulating properties, or sound absorbency. Thus, such glass wool molded products are widely used in various fields such as in heat insulation materials used for building materials, in heat insulation materials used for automobiles, in refrigerators, or in freezers, for the purposes of thermal insulation, cold insulation, heat shielding, sound insulation, etc.
In general, soda lime is singly used as a material glass in production of a glass wool. Otherwise, an alkali borosilicate glass produced by adding several percents of boric acid to the soda lime is also used as such a material glass.
In order to produce a glass wool using the aforementioned material glass, for example, the material glass is thermally melted by high-speed rotation of a spinner having a large number of pores on the lateral face thereof, and the thus melted material glass is blown off in a fibrous state, so that the material glass can be air-cooled to obtain a glass wool. When the thus obtained glass wool is processed into a felt-like, board-like, or pipe-like molded product, immediately after the material glass has been processed into fibers, a small amount of binder is sprayed on the surfaces of fibers so that it can be applied thereto. In general, as binders used in the molding of glass wools, organic binders such as a phenol resin, an epoxy resin, an acryl resin or starch, and inorganic binders such as liquid glass, boric acid or colloidal silica, have been known.
In production of a vacuum heat insulation material used in a refrigerator, for example, the handling ability of a glass wool molded product used as a core or the smoothing properties of the surface of the vacuum heat insulation material can be improved by addition of a binder. However, if such a binder is used, the cost of the binder as a material and the number of production processes increase to lead to increases in capital investment spending and energy consumption, and as a result, the production cost is also increased. In addition, in the case of a vacuum heat insulation material, there are the following problems. That is, if an organic binder is used, the degree of vacuum is decreased due to volatile substances from the binder. On the other hand, if an inorganic binder, particularly, boric acid is used, the degree of vacuum decreases due to volatilization of bound water, so that the vacuum heat insulation material cannot maintain its heat insulation performance. Accordingly, when a binder is used, in order to stabilize the performance of a vacuum heat insulation material for a long period of time, it is necessary to increase the amount of a gas adsorbent or addition of high performance adsorbent (which is expensive). Such factors also cause cost increase. Moreover, in general, the use of an organic binder is also problematic in that the heat resistance of a glass wool is 350° C. at maximum.
Thus, a felt-like product that contains no binders has been proposed as a means for improving heat resistance. Such a felt-like product is resistant to a temperature between 400° C. and 450° C. In the case of producing a vacuum heat insulation material, for example, a glass wool used as a core generally has an area density between 1500 and 3500 g/m2, and thus it has high heat insulating properties. However, if glass wools are only compressed without adding binders in the aforementioned method, the obtained glass wool product has a thickness between 70 and 100 mm. Further, the product has not been sufficiently molded, so that it is problematic in terms of extremely poor handling ability.
For the aforementioned reasons, various methods for producing a glass wool molded product with good handling ability without using binders have been developed. For example, Patent Document 1 describes a production method, which comprises subjecting glass wools to press molding at a temperature higher than the temperature at which the glass wools are thermally deformed, so that an aggregate of glass fibers can be subjected to plastic deformation in a pressurized state, thereby maintaining the form thereof.
Moreover, Patent Document 2 describes a method of molding laminated glass white wools (which are glass wools that contain no binders) within a temperature range that is 20° C. higher than the deformation point thereof.
Furthermore, Patent Document 3 describes a core formed by the adherence of inorganic fibers as a result of an intermolecular interaction caused by Si—OH groups.
Patent Document 1: Japanese Patent No. 3580315
Patent Document 2: National Publication of International Patent Application No. 2003-532845
Patent Document 3: Japanese Patent No. 3578172
In Patent Documents 1 and 2, however, since press molding is carried out at a temperature higher than the thermal deformation temperature of glass wools, the tensile stress on the fiber surface is alleviated, and thus the fiber strength is significantly decreased, so that the glass wools can easily be converted to powders. As a result, there is concern that problems regarding a decrease in handling ability during the production process or deterioration in work environment will occur. Moreover, there are also various problems caused by the release of fibrous powders during the recovery and recycling processes of a vacuum heat insulation material.
Furthermore, in the vacuum heat insulation material of Patent Document 3, adhesion of inorganic fibers is insufficient, and thus there is a problem regarding a decrease in handling ability due to the molded material returning towards its former state after compression.